nbcnews.com/wwyd. of course you can always join in on the conversation on facebook and twitter. i'm john quinones. "20/20" starts right now. i did not cause my mother's death. i love my mother. present tense, i love my mother. >> he was definitely our prime suspect. >> tonight, a bigami mystery, a missing mother. her grown son, lost at sea. then found, seven days later. a real-life castaway. but with one big difference -- is it missing at sea, or murder at sea? >> can you understand what people see? you were the last person to see people alive. tonight, "20/20" investigating an ongoing case. with the only reporter to sit down with the son. >> do you think police have

picked on you? >> i think they saw me as the lowest-hanging fruit. >> but targeted because of his diagnosis, or is there something suspicious going on? now, with an unsolved murder in the family's past and new information in the case, what really happened? >> they want to explore whether or not you sank the boat on purpose. >> we're done here this evening. >> lost at sea. >> good evening, i'm amy robach. david muir is off tonight. suspicions continue to swirl around this story. linzie janis, how she got this exclusive is a story all its own.

>> reporter: my name is devin. i work the overnight shift at abc news. on the night of september 26th, i saw that one of the affiliate reporters had tweeted about someone who had been rescued at sea. i sent it around, but, you know, of course we didn't have too many of the details besides that he had been found. >> he was found in a life raft, with a life jacket on. he was reported to be in good condition. >> reporter: they sent linzie janis. >> linzie janis. >> linzie janis has that story for us. >> reporter: the freighter he is on is due to arrive in boston. when i first heard about the nathan carmen story, it looked like an inspiring story of survival. >> the son rescued off martha's vineyard. >> reporter: nathan had gone out on this fishing boat with his 54-year-old mother linda and never returned. the coast guard combed hundreds of miles of ocean in vain and they'd just given up hope when the call came in. a young man found alone floating on a life raft. >> found alive in good condition. >> reporter: the stunning discovery made in the open ocean

by this chinese freighter carrying scrap metal, about 100 miles south of ram point marina in rhode island, where he'd set sail. they'll get the chance to speak with nathan carman tuesday night. >> nathan, this is u.s. coast guard boston. i need to understand what happened. >> reporter: yeah, we all do. but so far, the only explanation, this short radio call from the coast guard to nathan aboard that freighter. >> mom and i, two people. myself and my mom were fishing at block canyon. and there was a funny noise in the engine compartment. when i saw the life raft, i did not see my mom. have you found her? >> no, we have not been able to find her yet. >> reporter: the next day, nathan arrives in boston. the questions waiting for him at the dock. >> the most important question is, how did you survive and not your mother?n we f

him, he shows little emotion. his 6'3" frame awkwardly appareled in the white crew suit he was given after his rescue. that night, nathan returns to his home in rural vermont and makes his first public statement. >> i would just like to thank the public for their prayers and for their concern for both my mother and for myself. emotionally, i've been through a huge amount and my request is just to be allowed to mourn naturally. >> reporter: it seems that's all he has to say. but then nathan decides to grant us an exclusive interview. he instructs us to meet him on this bench. he seems anxious, traumatized. >> i'm not sure how best to say this. >> reporter: worried he won't look or sound good on camera. >> oh, lord, may you help us to -- >> reporter: he even prays about it. >> -- to help me to accurately

and effectively express what i have been through. >> reporter: there's a reason nathan doesn't speak in the tongues of angels. he has been diagnosed with asperger's syndrome, which is on the autism spectrum, associated with social awkwardness and flat, measured speech patterns. let's begin, if we could, with the fishing trip. our conversation will last into the night but it ends up a fragmented account with plenty of blank spaces. >> i'm not going to go into that now. i'm not going to answer that. i'm not going to go there. >> reporter: but nathan is able to provide more details about that ordeal at sea. >> my mom and i fished very frequently together. that's the primary thing we did to spend time with one another. we fished probably every other week. >> reporter: despite his humble appearanceitur england family. the first of many surprises. his mom linda, a nurse who worked with autism patients, didn't even like to eat fish.

but she loved catching them with nathan. in this facebook posting, she said, "there was no better way to connect." nathan had purchased this 31-foot fishing boat, named the chicken pox, after seeing it advertised online. he says that on september 17th, he and his mom set out for that fateful trip just before midnight. these fishing trips, you would often leave, what, at night or in the early hours of the morning? >> that's correct. we met at the marina in rhode island, got all of our gear on board, pushed off from the dock. >> reporter: nathan wanted that night to be different. he says that instead of the usual trip of about 20 miles to block island for striped bass, he decided to go deep sea tuna fishing, to that area called "block canyon." that's much farther offshore. >> that's offshore fishing. >> reporter: it takes all night to get there. the sea bed here drops from a few hundred feet below the

surface to 1,000 feet or deeper. a perfect spot for those giant tuna they were after. >> i have experience boating. i have experience fishing. i did not have experience offshore fishing. >> reporter: but nathan was comfortable making the trip because, he says, the seas were calm after a smooth cruise through the night. >> we arrived just as the sun was rising. >> reporter: nathan says the new day was perfect. they set their lines and fish for tuna, all by themselves. they have life vests onboard, but weren't wearing them. hours passed. it was midday when he says the trouble started. so what happened? what went wrong? >> i heard a noise. >> reporter: a funny noise coming from the engine. >> the engine sounded different. i looked in the hatch where the engine was, i observed there was water. quite a bit of water. the belt on the engine was picking up water and kind of spinning it.

>> reporter: what did you think? >> i knew there was a serious problem. but i didn't think we were sinking. i thought i was going to diagnose the problem and that we were going to go back to shore. >> reporter: he says he closed the hatch and shut off the engine. he says he told his mother to gather the fishing lines in the rear while he says he brought the ditch bags full of safety gear up to the front. but he says to his shock, in no time the boat was under water. >> i was walking on the deck. it was there. and then it wasn't. >> reporter: any sign of your mother at this point? >> no. not at that point. >> reporter: he claims he was totally disoriented. doesn't remember hearing his mother or seeing her. the life raft was designed to inflate automatically. nathan says he swam to it. >> i got onboard the life raft and was looking around and i was calling out to my mom. i did not see or hear my mom. i was blowing the whistle with

three loud, short bursts, which is a distress signal. >> reporter: so if she had been on the surface of the water, you feel like you would've been able to see her? >> i assumed that if she had been on the surface and conscious that she would've been calling out to me and i would've been able to find her. but i didn't know why that hadn't happened. >> reporter: now, by his account, he was all alone in a kind of floating tent. a tiny speck of orange in a vast grey sea. as that night fell, he was drifting in the darkness. like tom hanks in "castaway," nathan says he spent days alone out in the open water until, just like the movie, the freighter that saved nathan, aptly named the orient lucky, was docked when we intercepted it later that week. they'd recorded this remarkable footage of the rescue. look here, that little figure is

nathan, clinging to a life preserver, clinging to life, then jumping into the churning seas. as the ship struggles to stay close enough to grab him. >> we could see he was very tired. exhausted. he rested for a while clinging on to the ladder. our crew helped him to get onboard our ship. >> i was no longer lost and that's when i allowed myself to feel relief. >> reporter: what was going through your mind? >> i'm safe. >> reporter: it's a compelling, heartstring-tugging story of loss and survival. >> that i love my mother, present tense, i love my mother. >> reporter: but is it also something more? >> police want to know, what role, if any, nathan carmen played in his mother's disappearance. >> wait a second. was this just an accident? >> reporter: is his story really the whole story? as more details emerge, the portrait of the young fisherman takes on a darker hue. >> it paints a very troubling picture as to what was nathan's intent.

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>> reporter: nathan carman was found floating on a life raft in the ocean. >> reporter: two members of the carman family went out to sea. only one came back. so why are people so suspicious about what exactly happened to nathan's mother linda? >> now officials are investigating just how the 31-foot boat sank. >> rort spicion deepens as we learn that the mother/son relationship could be as choppy as the north atlantic. >> well, i think anyone who has a child that has autism or asperger's, it's difficult. there were conflicts on occasion, but he considered her his best friend. >> reporter: in addition to any personal friction, investigators

see a possible financial incentive for foul play. is nathan due to get a huge windfall? is he due to get all of his mother's money? >> that's my understanding. >> reporter: millions of dollars? >> yes. think it's around $7 to $8 million. >> reporter: that's why a phalanx of investigators -- local police, the coast guard, even the fbi -- are taking a hard look at signs of possible criminal activity on that doomed boat. and so are we. this is ram point marina in rhode island, where nathan and linda set sail that night in september, 2016. >> welcome aboard. come on in. >> reporter: captain dave mccormick runs irish jig charters and was out fishing the day nathan and his mother set out on that seven-hour trip to block canyon. captain dave considers it highly unusual for a mother and son to fish alone for tuna. those fish can weigh hundreds of pounds. >> there's usually a crew of four, and it's usually all experienced guys. >> reporter: usually a crew of

four experienced fishermen. >> usually. you know, to be smart about things. >> reporter: on top of that, captain dave says a 31-foot boat like the chicken pox would be too small a vessel for even the most experienced fisherman. and remember, nathan had never done this before. first time you're taking your boat that far offshore? >> that's correct. >> reporter: captain dave is also puzzled by nathan's actions after he says he reached block canyon and realized the boat was taking on water. there was a functioning alert system onboard, but nathan never used it. how long does it take to activate or make a mayday call? >> it's just a matter of seconds. you just flip the switch, and it's activated if it's a manual type. >> reporter: the coast guard said there was no mayday call. did you have a radio on the boat? >> i had a radio, and there was also an emergency position-indicating radio beacon. i didn't know that we were sinking. i knew that we had a problem,

but i didn't know that we were sinking until we sank. >> if you look at nathan's behavior, if you take all of those things collectively together, it paints a very troubling picture as to what was nathan's intent and what actually did happen to his mother. >> hello, this is nathan carman. >> reporter: and what to make of nathan's seemingly odd behavior after he was rescued? just listen to his call with the coast guard. >> so i got to the life raft after i got my bearings, and i was whistling and calling and looking around and i didn't see her. >> reporter: nathan's affect is as flat as pavement as he recounts the tragic loss of his mother, asking about her seemingly as an afterthought. >> when i saw the life raft, i did not see my mom. have you found her? >> reporter: but wait before you judge. psychologist dr. rebecca sachs says people with asperger's

often speak without emotion, and order their thoughts in a way others might find unusual. >> picking out what is the most important piece of information is often really, really difficult. they'll sort of give information in a linear fashion. >> reporter: so you're saying that it's not necessarily unusual that he didn't lead with, "my mother is missing"? >> correct. >> reporter: sachs has never treated nathan, but says people with asperger's affects how he interacts with others, and can lead to misunderstanding. take what happened at this donald trump rally in new hampshire, which nathan attended just weeks before his mother's disappearance. nathan -- who told us he's a big trump supporter -- was removed from the rally after the man who took this photo reported him to security because he said he was uncomfortable with nathan's demeanor. and now, watch this odd moment during our interview when nathan reveals his mother needed coaxing to go on that fishing trip at all. she was concerned about safety? >> that's correct. it was not an argument.

i was kind of pestering my mom. she had always been kind of skittish -- we're stopping right here with that question. >> reporter: oh. okay. out of nowhere? >> stopping right there. >> reporter: and it's like, what happened? >> i sometimes talk about this need to control things. or thinking they know how to guide a situation or guide a conversation. i think that's just an impression that comes off. >> reporter: so maybe some of that seemingly defensive or suspicious behavior can be explained by nathan's conditions. during our interview, it's hard to get a full picture of him, in part because he's on edge after a crowd of media gathered, hoping to get to speak with him. as he got back in his truck, i head back to new york, haunted by one question. just who is nathan carman anyway? it's time to dig deeper for an answer. time to explore some dark and troubling secrets of nathan's

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>> reporter: back in the newsroom, the world keeps turning. a deadly train accident in new jersey. >> images of chaos and panic.

>> reporter: hurricane matthew batters the southeast. but i can't forget about the lonely young man up in new england. our interview made headlines. but so much was left unsaid about nathan's past, about how he survived, and as the days go by, the swells of suspicion are bearing down on him like a nor'easter. >> you've got to presume that he's thinking, "i'm going to tell my story, i'm going to put it out there, it's going to end this." that's not what happened. >> reporter: and then, surprise. 193 miles. nathan invites us back to vermont for a second interview. we're hoping this time he'll fill in some blanks. when we arrive at his home -- hi, nathan, how are you? nathan seems as adrift as he was out in the ocean. >> i was lost at sea, my mom died. what would be great, to have people embracing you, saying we

are glad you are home, we are glad you are alive and also helping me to deal with my mom's death. it hasn't been that. >> reporter: nathan says he was counting on support from linda's three sisters, his aunts. instead, there's been a stony silence. >> i haven't received any calls. >> reporter: not from a single one of them? >> that's correct. it makes me feel like i have no family. i want to have family, i want them to be my family. >> reporter: nathan's aunts don't want to speak with us either. >> it's a terribly, terribly upsetting and difficult time. their focus is not on relationships, it's on getting answers to questions. >> this barn may be from well before 1850, i don't know. >> reporter: wow. despite whispers he might have killed his mother for millions of dollars, nathan is hardly living the lush life up here. he spends days his renovating this house, hoping to fl it e ringtime. so far the only interested parties to come knocking have been the police, searching for

evidence of a crime on the high seas. >> the 22-year-old's demeanor was strange. >> reporter: driving around with nathan, he seems unfazed by the police attention. had your mom come up to visit you here? >> yes we, she drove up to the area frequently. and we saw each other. >> reporter: he says he called us back to set the record straight because so much of what he's seen on the news has been unfair. >> right this way. >> reporter: this is not easy for nathan. >> i am not someone who understands relationships or who is good at talking about emotions. >> reporter: but he's willing to try. as he opens up a bit, it's clear, he's had a hard life, the loneliness he's feeling now is nothing new. in fact, it's been a lifelong companion. a gut 1 mil south of here, in middletown, connecticut, a suburb of hartford. an only child from a broken home. his parents divorced when he was very young and for most of that

time, his mother linda was everything to him. what was she like? >> she was a good person, a warm person. we did have a challenging relationship at one point in my life, but she was the only family who i really had and now i don't have her and that's a tremendous loss. >> reporter: you feel alone? >> yes, when i had her i didn't feel alone. >> considering she was the most important person in his life, the most important and fundamental question is, would he really have wanted to kill her? >> reporter: another port in the storm, this man. his grandfather, linda's dad, john chakalos. a multimillionaire real estate and nursing home developer. >> he was like a father to me. and i know i was like a son to him. >> reporter: they ate dinner together regularly at grandpa's house and there were even numerous take your grandson to

work experiences when chakalos carted young nathan to business meetings with his associate pat goggins. >> i got the feeling that john had a very good relationship with him and was trying to cultivate that. nathan was as introverted as john was extroverted. >> reporter: not surprisingly, that introverted personality trait did not go over big at middletown high school, where classmates recall him being mocked. but he did have one close friend. a beautiful white horse named cruise. lucky you, having your own horse. >> yes, i was fortunate in that regard and i was able to really form a strong bond emotionally. >> reporter: but when nathan was 17, cruise died and nathan's fragile world fell apart. shortly after cruise died, you ran away from home.askingouor your help, they're trying to find a missing teenager from middletown. >> patrol officers have all been briefed to keep a lookout for nathan carman. >> reporter: nathan had been spotted taking a bus. teams of searchers looked for him for days. >> running away from home is

something that i felt i had to do at the time. i don't fully understand it or comprehend that sitting here now. >> reporter: he was eventually found nearly 600 miles away in rural virginia. when he returned home, nathan was reportedly hospitalized briefly for mental health issues. when you returned home after you had run away, when you were found? >> yeah, that gets into my personal health records, which i am not going to disclose or discuss. >> reporter: did things get better or did they get worse? >> i can't answer that question and we're done with that before i turned 18. >> reporter: nathan was released and for a time, whatever storm was raging inside of him subsided. but for how long? >> he was found shot and killed. >> reporter: coming up, the holidays turn bloody as grandpa chakalos is gunned down just before christmas. and the police want to know, did his quiet, beloved grandson pull the trigger? >> yes, nathan was a suspect in the murder of his grandfather. >> reporter: stay with us.

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>> reporter: christmas in new england, and people come from miles around to see this elaborate light display. john chakalos puts up at one of his many properties, but the holiday spirit ends abruptly on the violent night of december 20th, 2013, when the real estate millionaire is found shot to death in his connecticut home. authorities say execution-style. >> one of his daughters had gone to check on him, and found him in his bed with what looked to

be gunshot wounds to his head and back. >> police are now calling the shooting death of an 87-year-old man a homicide. >> reporter: who would want john chakalos dead? >> it's a very good question. >> reporter: at first police wonder, could it have been his daughter linda? there are reports of a big fight over the family fortune that got violent, linda punching and kicking her father. >> in the investigation, it has to be a relevant question to ask, "is that incident connected to what happened to him?" >> reporter: but a lie detector test clears linda. so, logically, cops focus on the last person known to see chakalos alive, none other than his beloved grandson. nathan had no obvious motive to gun down his granddad, but he had opportunity. the two had dinner together earlier that evening but police say nathan's whereabouts later that night are unaccounted for. >> the authorities wonder, "could that have been the time when he committed a murder?" >> reporter: and, according to

this search warrant, there is a litany of other circumstantial evidence. it says nathan discarded both the hard drive of his computer and the gps unit used on the morning of december 20th, 2013, that he had recently bought a .308 caliber rifle, the same caliber weapon used in the homicide of john chakolas. coincidentally, neither nathan's rifle nor the murder weapon were ever found. is it fair to say he was your prime suspect? >> yes, that is fair to say. he was definitely our prime suspect. >> reporter: police say that after john chakalos' murder, linda's sisters were afraid enough to hire armed security to protect them in their homes. were they afraid of nathan? >> john chakalos was murdered in cold blood in his bed, in his home. it would be irrational not to feel some fear as a result of that. >> reporter: with regard to the murder of nathan's grandfather, isn't the circumstantial evidence there strong? >> well, if it were there and it were strong, they would've

arrested him. >> reporter: that search warrant has a list a mile long of things that make nathan look suspicious. >> you can't arrest anybody in america on mere suspicion. you have to have probable cause. >> reporter: is there any truth to any of those allegations? >> no, there was not any truth to any of the allegations. >> reporter: nathan adamantly insists he's innocent. he says when the police came to interview him, he never tried to hide anything. >> if they had asked me, "nathan, can we look at your hard drive," or, "nathan, can we have your gps," at that time when they were in my apartment, my answer would have been, "sure, gladly. you can take it." but they didn't. >> reporter: do you think the police have picked on you? >> i think the police saw me as the lowest hanging fruit after my grandfather died because they saw that i had been diagnosed with asperger's. >> there's an element here of prejudice against nathan,

because of his disability, because when the police talked to him, they immediately become suspicious because of his odd manner. >> reporter: in fact, experts tell us people on the autism spectrum are more likely to be victims of crime than perpetrators. >> my understanding is that if you lie to the police and they can prove that you lied to them, they can arrest you for that, and they haven't done so. >> nathan remains a suspect in the murder of his grandfather. the investigation is actually very active at the moment, and ongoing. >> reporter: in january, 2017, law enforcement went back to the scene of the crime. the fbi also conducted a separate search elsewhere. >> the fbi and other agencies thisbaon newampshire gents g murd wean.y the fa but it's not just the investigation into his grandfather's murder hanging over nathan's head. the inquiry into his mother's

disappearance at sea is also steaming ahead. suspicious new details have emerged, allegations of sabotage. >> whatever he was doing was wrong. >> reporter: allegations nathan would rather not discuss. i'm just asking you to defend yourself against these people who are saying that you did something to your boat that would make it sink. >> we're done for this evening, period. we're done here. >> reporter: we're not trying to make you uncomfortable. why is nathan so agitated? >> we're done here. >> reporter: it is his condition? the suspicions about him? or a guilty conscience? ♪ ♪ i don't care where we go ♪ and i don't care what we do ♪ just take me with you there are roadside attractions. and then there's our world-famous on-road attraction. the 2018 glc. lease the glc300 for just $459 a month

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>> reporter: no matter what nathan carman says, the fog of suspicion isn't lifting. can you understand what people see? you were the last person to see two people alive. you are either incredibly unlucky, the most unlucky guy, or you had something to do with those two deaths. what do you say to that? >> i say there is no relationship between my having been the last person other than the killer to have seen my grandfather alive and my having been on the boat with my mother when it sank. i did not kill my grandfather. i did not cause my mother's death. and i want people to know that. >> reporter: nathan may sound sincere. but is he credible? >> the story makes no sense. supposedly, the boat springs a

leak, and no one can say, "hey mom, you want to join me on the raft?" there are too many questions without answers and too many answers without justice. >> reporter: when we ask nathan what happened to cause the boat to sink, he says he simply doesn't know. >> i am not a diesel engine mechanic. that's the most basic way that i can respond to it. >> reporter: but the police aren't buying that. they executed a search warrant of nathan's home, looking for evidence of reckless endangerment. noting that nathan had been seen doing repairs on the boat that potentially rendered it unsafe. boat owner mike iozzi bumped into nathan on the dock just hours before his fishing trip and told police that he saw nathan doing something highly suspicious. >> it kind of caught my eye when i saw him leaning over the back and drilling two holes in the transom of the boat. >> reporter: drilling holes? mike was dumbfounded.

he says nathan told him that he was removing stabilization devices like these, something called trim tabs. mike says that made no sense. >> you don't have to drill a hole to take the trim tabs off. why would you drill a hole in the boat? whatever he was doing was wrong. >> i am not sure how i can respond other than saying, he says one thing and i say this is what actually happened. >> reporter: nathan categorically denies any suggestion that he sabotaged the boat. he admits removing the trim tabs, but claims he patched the holes properly with marine putty. when we press him, he reaches a breaking point. >> all i can say is what happened. if other people want to -- >> reporter: i'm just asking you to defend yourself against these people who are saying that you did something to your boat that would make it sink. >> that's not true. >> reporter: okay. another thing that's happened since we last got together.

the police searched your mom's home. did you know anything about that? >> yeah, we're done for this evening, period. we're done here. >> reporter: we're not trying to make you uncomfortable. we're trying to give you an opportunity to answer some of these allegations. >> we're done here this evening. >> when someone gets up from an interview, calls it off, typically you think, person can't deal with the heat. questions are too tough. but maybe there's another explanation here. and that is his medical condition. >> a person with autism may not understand exactly all the social rules of what may happen. how maybe their instinct to react may not always be the most appropriate. >> reporter: sure enough, about 20 minutes later, nathan is ready to sit back down as we probe one final, highly curious part of his story. namely, what exactly happened during those seven days on that life raft?

most people would panic, nathan. most people would think, i'm going to die out here. >> and the way i handled that was to focus on what i had to do in order to survive. >> reporter: nathan says he had fresh water packets in his survival bags as well as kits to allow him to drink sea water. he also had food bars. he says he allowed himself only one each day. >> here we go, wilson. you don't have to worry about anything. >> reporter: in "castaway," tom hanks talks to a volleyball he names wilson. >> wilson! wilson! >> reporter: nathan says he talked with god. >> i prayed in the morning. and i prayed in the evening. >> reporter: that made you feel less alone. >> that was very comforting. >> reporter: of course, those prayers were answered when the orient lucky appeared. and after a week at sea, the miracle was complete. or was it? so if you were 100 miles offshore, you'd want a bigger

life raft. a better life raft? >> a better life raft, yeah. >> reporter: jim o'conner sells life rafts for a living. and he says nathan's account just doesn't hold water. nathan says he was in that life raft for about a week. does that sound survivable to you? >> barely. it happens. it has happened. but the life raft was not the type of life raft that somebody would normally survive a week in the conditions he was in. >> reporter: nathan says the seas were calm sometimes. and then very rough. with waves as high as 13 feet. he says he would close the door and ride it out. >> i expected the life raft to flip over at some point, just because you're in a small life raft in big seas. >> reporter: but o'conner says the type of raft nathan was in would have tumbled so violently he would likely have broken bones. >> he was in really good shape. for somebody who was in 13-foot seas in a small life raft, he was in remarkably good shape. >> reporter: what's the talk in your industry? what do people think?

>> that he might have not been out there for seven days. that he might have been in that life raft for a day or two. >> if the boat didn't sink on day one, and sunk on day four or day seven, that fundamentally changes the story. >> reporter: could nathan have drilled and filled those holes, sailed into open water, killed his mother, and then waited to scuttle the chicken pox until he saw the orient lucky coming over the horizon? >> he could have thrown her overboard, stayed on the boat for a while. we don't know exactly when that boat sank. >> reporter: it's easy to speculate about foul play. but proving it won't be smooth sailing. the wreck of the chicken pox may be 1,000 feet under water and without the evidence, it's hard to see anything more than a circumstantial case against nathan. >> well, i say, produce the evidence.

if you don't have the evidence, please keep your mouth shut, because you're ruining someone's life. >> reporter: but wait. >> new information tonight in the case of a mother/son fishing trip. >> reporter: one group of investigators says they have come to a conclusion. nathan puts his mother to rest, but not the nagging questions. >> have police told you anything about the status of the investigation?

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nathan's three aunts. why didn't linda's sisters attend the memorial service that nathan organized? >> they didn't feel it appropriate to have a memorial service when we don't know what happened. >> reporter: are linda's sisters afraid of nathan right now? >> linda's sisters are afraid, as we all should be. there is a killer out there. >> i wish very much that my whole family could have come together to pray for my mom. i wish desperately that my mom was rescued. i hope that she will be found. now i'm going to drive off. >> what about your grandfather. >> i need to close my door. >> sorry, nathan. take care of yourself. >> reporter: in the midst of all this family dysfunction and the ongoing criminal investigation, the questions hang in the wintry new england air. if nathan did plan to kill his mother, why would he have risked his life in that raft, since he had no way of knowing he'd be

rescued? or was the multi-million dollar fortune he's now set to inherit from his mother motive enough to risk it? >> until these cases are solved, and proven that he didn't have some involvement, people are going to believe he's the only game in town, he's the right guy. >> reporter: but in january, 2017, shocking headlines. an insurance investigation blames nathan directly. >> the insurance company filed papers in u.s. district court, claiming nathan made incomplete improper and faulty repairs to the boat. >> reporter: the company won't pay his claim because it finds what nathan did was intentional, specifically removing part of the boat's structure and heading to sea with four inadequately filled holes. the insurance company believes that the boat sank because of nathan's actions. >> it's very troubling. >> reporter: small points out that investigators did not make a finding on what happened to linda. so far, there's been no response from nathan in court. we wanted to ask him not only about the investigation of the

fishing boat but also about that recent fbi search of his grandfather's property. so we've been trying to get a hold of nathan. he hasn't answered my texts, my voicemails. i'm going to give him one last call. >> the number you have called is no longer in service. >> reporter: he disconnected his phone. nathan has disconnected his phone. sealed in his fortress of solitude, cut off forever from the two people who loved him most, nathan carman may long be remembered as we first saw him. a riddle wrapped in a mystery inside a white crew suit. is he a cunning and remorseless killer, capable of killing his closest family members? or just a lonely, tragic figure who, like the rest of us, only wants to be understood? tonight, even after all our questions, the answers seem as remote and murky as the bottom of the ocean.

>> nathan never charged with murder, is facing a lawsuit from his aunts. they want to prevent him from getting any share of his grandfather's estate. we'll be following the story. from all of us at "20/20" and abc news, have a good night, and a great weekend.

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